Jihadi Abu Osama, who has been holed up with al-Qaida radicals for a year, claims it’s only a matter of time before the UK becomes an Islamic state.

He bragged: “There is nothing in Britain – it is just pure evil. If and when I come back to Britain it will be when this Khilafah – this Islamic state – comes to conquer Britain and I come to raise the black flag of Islam over Downing Street, Buckingham Palace, Tower Bridge and Big Ben.”

His outburst came as security chiefs warned of a new threat from suicide bombers hiding explosives up their bums.

A manhunt is under way for bombmaker Ibrahim Al-Asiri, who has created devices that can be implanted inside a person’s body. With no metal parts, they are virtually undetectable by airport scanners.

“The safety of the public must come first”

David Cameron

Officials fear Al-Qaida plans to smuggle them on to planes flying between Britain and America.

Saudi Al-Asiri, branded “an evil genius” by the US, has been training fanatics in Syria.

The chemistry student, 32, has already turned his brother Abdullah, 22, into a bomber but he failed to hit his target. He also masterminded underpants bomber Umar Farouk Abdulmutallab’s bid to blow up a jet on Christmas Day 2009.

The threat will spell woe for holidaymakers as airports increase security.